Smart Lock in Cold Weather: What Goes Wrong in Winter

The short answer

A smart lock in cold weather has three weak spots: the batteries, the motor that throws the bolt, and the door itself. Cold slows the chemistry inside a battery, so a lock that ran for months in the fall can warn of low power in January. Cold also stiffens grease and shrinks or shifts the door, so the motor works harder to slide the bolt, which drains the batteries faster still. Most winter smart lock trouble comes from those three, not from the electronics. In Milwaukee a smart lock installation starts at $99, a lock repair at $79, and we work 24/7.

How cold a Milwaukee winter gets

January is the coldest month in Milwaukee. Under the 1991 to 2020 climate normals from NOAA, the average January low is about 17°F and the average high about 30°F. The record low is minus 26°F, set in January 1982 and matched in February 1996. A lock on an outside door sits through all of it, and a door that faces the wind off the lake feels it most.

What the lock maker allows

Smart locks list an operating temperature range, and it is worth reading. Schlage, for example, rates the outside part of its Encode smart deadbolt from minus 31°F to about 151°F, and the inside part, where the batteries sit, from 14°F to about 120°F. The outside part is built for weather. The inside part is meant to stay in a heated room. A smart lock on a door between the house and an unheated porch, garage, or entry can put the battery side in the cold, and that is where trouble starts.

Batteries in the cold

Most smart locks run on AA batteries, usually four. Cold reduces how much power a battery can deliver at the moment the motor needs it, so the lock may report a low battery on a frozen morning and seem fine again in the afternoon.

Which batteries to use is a question for the lock maker. Lithium AA cells hold up better in cold. Schlage, though, recommends premium alkaline batteries for its electronic locks, because a lithium cell holds its voltage until the very end and then drops off steeply, so the lock's low battery warning comes too late to act on. Follow the instructions for your model, and change the batteries in the fall, before the first deep cold, whatever their reading.

When the motor strains

A smart lock moves its bolt with a small motor. In summer the bolt slides into the strike plate easily. In winter, wood doors and frames dry and shrink, steel doors contract, and frost can lift a step or a porch slab a little. Any of those can shift the bolt so it rubs the strike plate. The motor then pushes harder and longer, the lock may stall halfway and beep, and the batteries run down in weeks instead of months.

The fix is mechanical: adjust the strike plate or the door so the bolt slides in freely again. A lock that locks easily by hand with the thumb turn, with the door closed, is aligned. A lock that needs the door pushed or pulled before the bolt will go is not. Our lock repair visits include that adjustment.

Keypads, ice, and snow

A keypad on the outside can ice over after freezing rain or a sudden thaw and refreeze. Brush thin ice off gently with a gloved hand before entering the code. Do not pour hot water on a lock or a keypad: the water runs inside, then freezes again, and can damage the electronics. A shovel left against the door or a snowbank piled to the lock can push moisture into the keypad, so keep the area around the lock clear.

A frozen key cylinder

Most smart locks keep a key cylinder as a backup, and a backup that has not been used since spring can freeze or stick. Use the key once in the fall to make sure it turns, and keep it somewhere you can reach from outside, such as with a neighbor or in your car. If the cylinder freezes, a lock de-icer from a hardware store frees it. Avoid heavy oil in the keyway, because it thickens in the cold and collects dirt. A locksmith can clean the cylinder and lubricate it with a dry lubricant that stays loose in winter.

Wi-Fi and the app

A smart lock that talks to Wi-Fi or a hub uses more power than one that only talks to a phone nearby. In winter, that extra draw adds to the cold. If your lock reports a weak signal, the radio works harder and drains the batteries sooner. A plug-in Wi-Fi bridge or hub closer to the door can help, if your lock uses one. Auto-lock is convenient, but each extra lock cycle costs battery, so a door that bounces open and closed many times a day empties the batteries faster.

Locked out by a smart lock

If the batteries die completely, most smart locks have a backup: a key cylinder, or terminals where a 9-volt battery can be held against the keypad to power it long enough to enter a code. Check your lock's manual for which one it has before winter. If neither works, a locksmith can open the door. Our page on smart lock lockouts explains how that visit goes.

A short checklist before winter

• New batteries in the fall, of the type the lock maker recommends.
• The bolt slides in easily with the door closed.
• The backup key turns, and you know where it is.
• The keypad and the area around it are clear of snow and ice.
• The Wi-Fi signal at the door is strong, or the bridge sits close by.

If the lock fails any of these, we can adjust the door, clean the cylinder, or suggest a lock that suits your door better. Our page on smart lock installation shows the locks we put in.